Converter for high pressure synthesis

ABSTRACT

A converter for high-pressure synthesis of ammonia or methanol having an upright outer pressure shell consisting of three superimposed spherical segments and two interposed annular connectors, a thin-walled conforming liner in the shell, an upright conduit axially centered in the shell and extending from a grating in the lowermost segment close to a manhole atop the uppermost segment and barely big enough for insertion of the conduit therethrough. A body of particulate catalyst material fills the annular space between the liner and the conduit from the grating almost to the top end of the conduit. A shell-andtube heat exchanger is arranged in the conduit for preheating a portion of the gaseous reactants by means of the hot reaction gases. The remainder of the reactants is injected into the catalyst through perforated radial pipes extending from each connector toward the central conduit.

United States Patent [151 3,653,846 Kubec et al. [4 Apr. 4, 1972 s41 CONVERTER FOR HIGH PRESSURE 1,839,738 1/1932 Casale ..23/289 SYNTHESIS Primary ExaminerJames H. Tayman, Jr.

[72] Inventors: Jirl Kubec, Kunstat Na Morave; Vladimir Atmmey Richard Low Saroch, Brno, both of Czechoslovakia [73] Assignee: Kralovopolslta Strojirna, Zavody [57] ABSTRACT chemlckych milefliv modal Podnlk, A converter for high-pressure synthesis of ammonia or Czechoslovakla methanol having an upright outer pressure shell consisting of [22] Filed: 5, 1969 three superimposed spherical segments and two interposed annular connectors, a thin-walled conforming liner in the [211 App]. No: 84 ,66 shell, an upright conduit axially centered in the shell and extending from a grating in the lowermost segment close to a manhole atop the uppermost segment and barely big enough [52] CL for insertion of the conduit therethrough. A body of particu- [51] [In C] Bo1j9/04 3/00 late catalyst material fills the annular space between the liner [58] Fieid s {,289 2889l l and the conduit from the grating almost to the top end of the conduit. A shell-and-tube heat exchanger is arranged in the conduit for preheating a portion of the gaseous reactants by [56] References means of the hot reaction gases. The remainder of the reac- UNITED STATES PATENTS tants is injected into the catalyst through perforated radial pipes extending from each connector toward the central conl,408,987 3/1922 Casale ..23/289 duit 3,498,756 3/1970 Carson... ..23/289 1,478,550 12/1923 Casale ..23/289 4 Claims, 1 Drawing Figure Ida CONVERTER FOR HIGH PRESSURE SYNTHESIS This invention relates to con erters for high pressure synthesis, and particularly to a converter suitable for the synthesis of ammonia or methanol from a gas mixture at a pressure of the order of 4,000 psi. and at a production rate of 1,000 tons per day or more.

The conventional cylindrical converters cannot be scaled up to large unit output because the necessary outer pressure shells would become prohibitively heavy. Converters of at least partly spherical curvature have therefore been proposed, and offer substantial advantages over the earlier cylindrical converters, particularly when the pressure shell consists of several spherical segments.

In the known converters having shells of the multiple sphere type, the necessary cooling of the reaction zone is provided by means of heat exchangers at the annular connectors between the spherical segments. ln connection with this cooling arrangement, and for other inherent reasons, it was necessary to provide gratings at each connector and to divide the catalyst into several portions respectively carried on the gratings in the several segments.

When spent catalyst was to be removed from the known multiple-sphere converter, it was necessary also to remove the gratings, and a manhole had to be provided large enough to pass the gratings. The pressure exerted on the relatively large manhole covers sets a limit to the size of the converter. The manhole diameter could not be increased at will without causing structural difficulties and excessive cost for the manhole cover and the closure employed for holding it in place against the internal converter pressure.

The primary object of the invention is an improvement in the multiple-sphere type converter which pennits such a converter to be built at practical cost in unit sizes even larger than were possible heretofore.

It has been found that the heat exchangers employed heretofore at the connectors between the spherical segments can be replaced by other cooling means which permit the use of an axially continuous body of particulate catalyst material extending upward from a grating in the lowermost spherical segment in at least two and preferably all the segments of the pressure resistant outer shell of the converter, and to discharge the catalyst bed through chutes in the sole grating without any need for removal of the grating. This permits a substantial reduction in the size of the manhole to less than the internal cross section of the annular connectors which in turn is smaller than the cross section of the segments adjacent the converters.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following detailed description of a preferred embodiment relating to the annexed drawing.

The sole FIGURE of the drawing shows a converter of the invention in side elevation, and partly in axial section.

The outer pressure shell 1 of the converter is a unitary, welded, heavy steel body. lts inner wall is lined with a thinwalled, conforming metal liner 2 whose inner face carries a coating 3 of asbestos or similar thermally resistant material chemically inert to the reactant gases and to the catalyst employed under the prevailing reaction conditions. A manhole 21 at the top of the shell 1 is normally closed by a cover 4 heavy enough to withstand the operating pressure and held in place by conventional closure elements, not shown. A relatively light inner cover 5 similarly closes an opening in the liner 2 aligned with the manhole in the direction of the vertical converter axis.

The heavy pressure-resistant shell 1 consists essentially of three approximately spherically curved segments 18a, 18b, 18c, and two, identical, heavy connector rings 19 interposed respectively between the segments 18a, 18b and 18b, 18c and forming outwardly projecting reinforcing ribs. The segments and rings are joined to each other by welding into a unitary structure which is elongated and has a longitudinal, upright axis. The axial height of each connector 19 is only a small fraction of the corresponding dimensions of the connected segments, and the internal cross section of each connector is smaller than the cross sections of the connected segments perpendicular to the axis adjacent the connector.

A cylindrical conduit 6 extends coaxially in the cavity within the liner 2 from a horizontal grating 7 in the lowermost shell segment 18c near the converter bottom almost to the cover 5 in the topmost segment 18a. The annular space radially bounded by the lined shells l, 2 and the conduit 6 above the grating 7 is filled with a bed 8 of particulate catalyst material which forms a continuous body axially extending in the three segments 18a, 18b, 18c from the grating 7 practically to the top of the conduit 6.

The lower portion of the conduit 6 holds a heat exchanger 9 whereas the top portion is plugged by an electric heater assembly 10. A horizontal partition wall 1 1 divides the converter space in the segment under the grating 7 into two chambers sealed from each other. The shell 12 of the heat exchanger 9 is radially spaced from the enveloping conduit 6 and projects downwardly beyond the conduit and the grating 7 to a sealed connection with the partition 11 about an axial passage in the same.

Several tubular chutes 14, of which only one is seen in the drawing, lead downwardly and outwardly from the grating 7 through the partition wall 11 and the shell 1. They are normally capped and permit the catalyst material 8 to be drained from the shell 1 if open. The tube nozzle 15 of the heat exchanger 9 passes axially outward from the segment 18c and provides the principal inlet for the mixture of gaseous reactants. A discharge nipple 16 leads through the shell 1 outwardly from the lowermost chamber in the segment 18c.

A radial inlet duct 13 in each connector ring 19 is connected with an annular manifold pipe 20 extending along the inner, asbestos-covered face of the liner 2 in the passage of the ring 19. Perforated pipes 17, of which only one is seen in the drawing, are circumferentially distributed over the inner face of the manifold pipe 20 and extend from the manifold pipe as closely to the conduit 6 as is feasible in view of the necessary clearances for thermal expansion and contraction and the need for axially withdrawing the conduit 6 from time to time for maintenance purposes. The pipes 17 are spaced from each other sufficiently widely so as not to interfere with axial movement of the catalyst material when the shell 1 is charged with new catalyst or drained of spent catalyst.

The afore-described converter is operated as follows in the synthesis of ammonia from a gas mixture essentially consisting of nitrogen and hydrogen.

The gas mixture, suitably preheated and compressed, enters the converter through the tube nozzle 15 of the heat exchanger 9. The heat exchanger tubes provide a channel leading upward into the heater assembly 10 where the mixture is brought up to reaction temperature during a start-up period. The heated gas mixture flowing from the heater assembly at the top of the segment 18a passes downward through the catalyst bed of iron oxides and the gas-permeable grating 7 into the chamber above the partition 11, upwardly through the annular space between the wall of the conduit 6 and the heat exchanger shell 12 to the top of the latter, and ultimately through the shell 12 in heat exchanging contact with the tubes and the reactant mixture therein into the converter bottom and out of the converter shell 1 through the discharge nipple 16 for further recovery of its thermal energy in any desired manner.

The reaction of hydrogen with nitrogen is exothermic, and the temperature of the catalyst bed 8 is controlled by injecting a mixture of the reactants at ambient or other relatively low temperature into the reaction mixture through the perforated radial tubes 17. Although the tubes are relatively widely spaced, the freshly introduced gases are unifonnly distributed in the reaction mixture by being released over the entire flow section of the catalyst bed and in all directions from the perforations of the pipes 17. After a steady state is reached, the heater assembly 10 is no longer needed, and may be deenergized.

When the catalyst is spent and needs to be replaced, it is drained from the chutes 14 without requiring a man to enter the shell 1, and fresh catalyst may be supplied through the manhole 21. It is normally preferred to vary the particle size distribution of the catalyst material in such a manner as to make the effective flow section of the bed 8 approximately uniform over its axial height. Thus, coarser particles are used in the narrow catalyst bed portions within the connector rings 19 and finer particles in the widest mid-sections of the three segments 18a, 118b, 180. The variation in particle size is readily achieved by sequentially feeding suitable catalyst fractions to the manhole 21. Obviously, other variations in the composition of the several axial portions of the catalyst bed 8 may be made without installing intermediate gratings which would interrupt the axial continuity of the bed.

The conduit 6, heater assembly 10, and heat exchanger 9 may be withdrawn from the coverter shell 1 by means of an overhead hoist in a very simple manner if repairs should become necessary. The liner 2 does not normally need to be removed, and be to removed, and damage to its thermally resistance inner coating 3 may be detected and repaired in the shell 1 since the coating is easily accessible after removal of the catalyst bed 8 and of the conduit 6 and its contents.

The illustrated shell segments 18a, 18b, 18c have the same radius of curvature, but shell segments differing in their radii of curvature may be employed if desired, and the radius of curvature particularly of the central segment may be chosen so that the shape of the segment closely approaches that of a cylinder. Not less than two approximately spherical segments are required for the apparatus of the invention, but more than three may be used in an obvious manner.

While the operation of the apparatus has been described with specific reference to the synthesis of ammonia, the apparatus may be used without modification for synthesizing methanol from a gaseous mixture of reactants, and adapted for other purposes without departing from the scope and spirit of this invention.

We claim:

1. A converter for high pressure synthesis comprising, in combination:

a. a pressure-resistant, outer shell, 1. said shell being elongated and having a longitudinal, upright axis,

2. said shell being fonned of a plurality of axially consecutive, substantially spherically curved, hollow segments having integral flanged end portions, comprising an annular connector interposed between each pair of axially consecutive segments and forming reinforcing ribs for said shell,

3. the axial height of each connector being much smaller than the axial height of the connected segments, and the internal cross section of the connector being smaller than the cross sections of the connected segments transverse to said axis;

b. a gas permeable grating in the lowermost of said segments, the uppermost segment being formed with an axially directed manhole having a cross section smaller than each of said internal cross sections;

c. a conduit of substantially uniform cross section smaller than said manhole located on a longitudinal axis in said shell and extending through each of said segments from said grating to said manhole, said shell and said conduit radially bounding an axially continuous annular space from said grating to said manhole,

(d) a continuous body of particulate catalyst material located in said space upward from said grating through said space in at least two of said segments; and

e. a heater arranged within the upper portion of said conduit, permitting a flow of gas into said catalyst material,

f. a heat exchanger axially spaced from said heater in the lower portion of said conduit and connected thereto for serial flow of fluid, said heat exchanger defining two coaxial thermally connected, separated flow channels between itself and the walls of said conduit, the radially outermost one of said channels communicating with the catalyst material;

g. feed means for feeding a gas through said heat exchanger to said heater to be reacted to;

h. discharge means for withdrawing a reacted gas from the radially innermost one of said channels.

2. A converter as set forth in claim 1 further comprising cooling means for cooling the body of catalyst material, said cooling means including a plurality of circumferentially spaced, apertured distributor conduits extending towards axis within each of the connectors and the flanged end portions of each pair of segments and supply means for supplying a gas to said distributor conduits.

3. A converter as set forth in claim 2, further comprising a liner conforming to the inner wall of said shell, said liner having an inner face directed toward said body of catalyst material, the cross section of said inner face in all planes perpendicular to said axis being greater than the cross section of said manhole.

4. In a converter as set forth in claim 3, a coating of heat resistant material on said inner face. 

2. said shell being formed of a plurality of axially consecutive, substantially spherically curved, hollow segments having integral flanged end portions, comprising an annular connector interposed between each pair of axially consecutive segments and forming reinforcing ribs for said shell,
 2. A converter as set forth in claim 1 further comprising cooling means for cooling the body of catalyst material, said cooling means including a plurality of circumferentially spaced, apertured distributor conduits extending towards axis within each of the connectors and the flanged end portions of each pair of segments and supply means for supplying a gas to said distributor conduits.
 3. A converter as set forth in claim 2, further comprising a liner conforming to the inner wall of said shell, said liner having an inner face directed toward said body of catalyst material, the cross section of said inner face in all planes perpendicular to said axis being greater than the cross section of said manhole.
 3. the axial height of each connector being much smaller than the axial height of the connected segments, and the internal cross section of the connector being smaller than the cross sections of the connected segments transverse to said axis; b. a gas permeable grating in the lowermost of said segments, the uppermost segment being formed with an axially directed manhole having a cross section smaller than each of said internal cross sections; c. a conduit of substantially uniform cross section smaller than said manhole located on a longitudinal axis in said shell and extending through each of said segments from said grating to said manhole, said shell and said conduit radially bounding an axially continuous annular space from said grating to said manhole, (d) a continuous body of particulate catalyst material located in said space upward from said grating through said space in at least two of said segments; and e. a heater arranged within the upper portion of said conduit, permitting a flow of gas into said catalyst material, f. a heat exchanger axially spaced from said heater in the lower portion of said conduit and connected thereto for serial flow of fluid, said heat exchanger defining two co-axial thermally connected, separated flow channels between itself and the walls of said conduit, the radially outermost one of said channels communicating with the catalyst material; g. feed means for feeding a gas through said heat exchanger to said heater to be reacted to; h. discharge means for withdrawing a reacted gas from the radially innermost one of said channels.
 4. In a converter as set forth in claim 3, a coating of heat resistant material on said inner face. 